The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.
Wireless communication system attempts to adjust cell coverages in order to avoid shadow areas which, however, happen in the real world environment due to buildings, underground tunnels or the like. Distributed antenna system (hereinafter abbreviated as “DAS”) has been used to provide service coverage to such shadow areas with multiple distributed antennas thereover.
Latest LTE and LTE-A services etc. are actively spreading, providing higher data transfer speed than the conventional 2G (GSM, CDMA) and 3G (W-CDMA). In LTE and LTE-A systems, Multiple Input Multiple Output (MIMO) technology is sought after for obtaining a high throughput in a limited bandwidth.
FIGS. 1A to 1D illustrate exemplary conventional DAS systems that do not support MIMO services. According to an example shown in FIG. 1A, a head-end unit is connected via a single coaxial cable to a remote unit which simultaneously provides a plurality of services via a plurality of relayed antennas. According to another example shown in FIG. 1C, the head-end unit is connected via a fiber optic cable to a hub unit which is connected to antenna-integrated remote units connected in a daisy-chain structure. Their services offered work in different frequency bands, and suffer from no mutual interference even if the services are propagated through one coaxial cable or one fiber optic cable.
The advent of MIMO technology has compromised this settlement. MIMO technology is to transmit and receive multiple MIMO signals sharing the common frequency band via multiple antennas. As a result, a distributed antenna system dedicated to Single Input Single Output (SISO), which is installed for the purpose of supporting 2G and 3G services, requires to connect LTE equipment supporting MIMO exclusively by 1T1R as in FIGS. 1A and 1C, or requires to install additional coaxial or fiber optic cables as in FIGS. 1B and 1D.